As integrated circuit semiconductor devices become more highly integrated, aspect ratios for contact holes used to interconnect conductive layers may increase. In other words, the ratio of a depth of the contact hole to a diameter of a contact hole increases. Accordingly, a metal providing a high degree of step coverage may be required to fill the contact hole to provide conductive interconnection between metal layers on opposite sides of the contact hole.
Accordingly, tungsten layers formed using chemical vapor deposition (CVD) and providing a high degree of step coverage have been used to provide metal interconnections. Such a tungsten layer can reduce the formation of voids in the contact hole.
FIG. 1A is a cross sectional view illustrating a metal interconnection according to the prior art including tungsten and aluminum interconnection layers connected through a contact hole. As shown, an insulating layer 12 is formed on a semiconductor substrate 10, and a tungsten interconnection layer 18 is formed on the insulating layer 12. Moreover, a conductive layer 16 including titanium nitride (TiN) and titanium (Ti) can be formed between the insulating layer 12 and the tungsten interconnection layer 18. A second insulating layer 14 is formed on the first insulating layer 12 and on the tungsten interconnection layer 18.
A contact hole is then formed in the second insulating layer 14 using photolithography and etch steps thereby exposing a portion of the tungsten interconnection layer 18. In particular, a dry etch can be used to provide a contact hole having a relatively high aspect ratio. A wetting layer 20 and an aluminum interconnection layer 22 are then formed on the second insulating layer 14 and on the exposed portion of the tungsten interconnection layer 18.
A subsequent thermal treatment may then be used to reflow the aluminum interconnection layer 22. The aluminum interconnection layer 22 and the tungsten interconnection layer 18, however, may react during this thermal treatment so that the volume of the tungsten interconnection layer 18 is reduced. In other words, the aluminum interconnection layer 22 and the tungsten interconnection layer 18 may react to form alloy regions 24a and 24b thereby reducing the portion of the tungsten interconnection layer 18 remaining. Because the alloy may have a higher resistance than that of tungsten, the resistance of the tungsten interconnection layer 18 may be increased.
FIGS. 1B, 1C, 1D, and 1E graphically illustrate EDX ingredient analysis in regions W, H, C, and F of FIG. 1A. As shown in FIG. 1B, there is no significant peak other than the peak of tungsten (W) for the region W of FIG. 1A. Accordingly, the alloy of tungsten and aluminum is not generated in region W. In FIGS. 1C, 1D, and 1E, however, there are aluminum peaks in addition to the tungsten peaks indicating that alloys of aluminum and tungsten are generated in regions H, C, and F of FIG. 1A. Accordingly, there continues to exist a need in the art for methods of forming metal interconnections with reduced alloy formation.